Art of desulfurizing diesel fuel and similar hydrocarbon fractions



Patented Nov. 7, 1950 2,528,587 ART OF DESULFURIZING DIESEL FUEL AND SIMILAR HYDROCARBON FRACTIONS John E. Ford, Jr., Garden City, N. Y.', assignor to Houdry Process Corporation, Wilmington, Del., a corporation of Delaware No Drawing.

Application August 20, 1947,

Serial No. 769,766

5 Claims.

This invention relates to the processing of petroleum crude oils containing such amounts of sulfur that the distillates therefrom contain commercially objectionable amounts of sulfur and is concerned especially with treating the diesel fuel fractions thereof so as to yield products having lower sulfur contents thanthe untreated straight run products. The term, diesel fuel fraction, as used herein, is a convenient term for fractions of a crude oil having boiling ranges between the initial and end boiling points of 50 to 250 F., these boiling ranges lying generally within the limits of from about 400 to 750 F. although, in some cases, the initial point may be as low as 350 F.

Many of the available crude petroleum oils have a sulfur content (sulfur contents are herein expressed in weight per cent) sufficiently high that the diesel fuel fraction produced by simple distillation of the crude oil has a sulfur content that is not commercially acceptable. This is particularly noticeable when the crude petroleum oil is of the type commonly known as a sour crude. Most of such crudes have a sulfur content of greater than 1 per cent in the 400 to 1000 F. fraction but it should be understood that the types and effect of the sulfur compounds present vary from crude to crude and that, although the above classification is convenient, the present invention includes the processing of crudes which have lower sulfur contents but which behave as sour crudes. In some cases, the sulfur contents of diesel fuel cuts from sour crudes are so high that blending such distillates with other diesel fuels having lower sulfur contents, such as those from low sulfur crude oils, to produce a blend of acceptable sulfur content is impractical. Chemical or extraction methods for the reduction of the sulfur content of diesel fuel fractions are costly and are apt to involve a considerable loss of the material treated. Existing catalytic processes are either expensive or have not successfully desulfurized petroleum fractions boiling in the range of 400 to 750 (the boiling range within which the diesel fuel fractions lie) without depreciating the quality of the treated fraction as a diesel fuel as measured by cetane number or diesel index. Likewise, thermal cracking is ineffective as a desulfurizing operation unless severe conditions are used; in which event, a low diesel index fuel is produced.

It has now been found, in accordance with the invention, that straight run or virgin diesel fuel fractions having objectionable sulfur contents, such as 0.5 per cent or higher, can be effectively desulfurized so as to reduce substantially the sulfur content of the hydrocarbon material remaining in the diesel fuel boiling range after the desulfurization operation by at least 25 per cent or more without substantially lowering or depreciating the diesel index or cetane number of such hydrocarbon material by contacting such straight run diesel fuel fractions with an active cracking catalyst of the type described below under mild conversion conditions selected to effect conversion of said diesel fuel fractions to between 10 and 30 volume per cent of gasoline (calculated on a butane-free basis). For brevity and convenience, this operation is referred to herein as desulfurization, and the zone in which it occurs as the desulfurization zone. It has been further found that particularly effective results are obtained when substantially all the hydrocarbon material charged to the desulfurization zone boils below the end boiling point of the diesel fuel fraction (i. e., the desulfurization may be effected in the presence of hydrocarbon material, such as gasoline which is lower boiling than the diesel fuel fraction being desulfurized, but hydrocarbon material higher boiling than the diesel fuel fraction should be excluded). It has been discovered that the diesel fuel fraction separated from the normally liquid conversion products of a desulfurization under the conditions described herein is a better fuel for a diesel engine than was the untreated straight run diesel fuel since the product from the desulfurization operation has a substantially lower sulfur content without any sacrifice in diesel index. Moreover, the gasoline produced from the straight run diesel fuel fraction as a result of the above operation is a high octane gasoline, having an octane number of '75 or more (CPR-motor method) without the addition of tetraethyl lead.

It is believed, although there is no intention to limit the scope of the invention to any particular theory, that the desulfurization of high sulfurstraight run diesel fuel fractions under the conditions set forth herein involves a different balance of the plurality of reactions that occur when hydrocarbon fractions are contacted with active cracking catalysts than does the usual cracking reaction. The presence of considerable amounts of sulfur in a hydrocarbon fraction has a considerable influence on the behavior of such a fraction when catalytically treated. The effect of high sulfur content is more clearly brought out when one appreciates that the content of sulfur-containing molecules is much higher than is indicated from the weight per cent of sulfur. For example, about 10 per cent of the total molecules are sulfur containing in a hydrocarbon fraction having a sulfur content of 1.4 weight per cent and having an avera e composition of C16 compounds (a typical diesel fuel fraction). It is believed that the presence of a considerable portion of such sulfur-containing molecules, particularly those of a cyclic nature, such as those of the thiophene or'thiophane type, result catalyst) in a lowered cetane number for the entire fraction. trast to diesel fuels prepared from the products of conventional cracking operations, where a considerable portion, and in some cases, all of. the diesel fuel fraction consists of hydrocarbons produced in the cracking process. The cracking operation produces, in addition to other hydrocarbons, unsaturates and aromatics, including those of the condensed ring type, whose cetane number is very low and are hence undesirable. Generally, the concentration of hydrocarbons that are undesirable as diesel fuel increases with increasing severity of cracking. It is believedthat the desulfurization conditions under which the straight run diesel fuel fractions are contacted with the active cracking catalyst, as described herein, are sufficiently severe that many of the sulfur-containing molecules are split but are not severe enough to cause formation of corresponding or a greater amounts of hydrocarbons having low cetane numbers. Thus, over a limited range of conditions, it appears that, in desulfurizations effected accordin to the invention, opposing reactions (the composition of low cetane number sulfur-containing compounds and the formation of low cetane number hydrocarbons) are balanced with the result that the cetane number of the resulting diesel fuel fraction is virtually unchanged, or, in some cases, is actually improved while, at the same time, the sulfur content is considerably reduced.

In general, the conditions under which the desulfurization operation is effective are selected from cracking conditions of temperature, pressure, contact time, catalyst activity and the like so as to limit the amount of the conversion of the diesel fuel fraction to less than about 35 volume per cent with the production of more than 10 and less than 30 volume per cent of butane-free motor gasoline or with fractions which are relatively low boiling or have only moderate amounts of sulfur, to less than 25 volume per cent. The selected combination of variables may be chosen from conditions which include temperatures in the range of 725 to 900 F., pressures in the range of about atmospheric to 25 pounds per square inch and space velocities in the range of 1.0 to 10 (where space velocity is defined as volume of liquid charged per volume of catalyst present in the reaction zone per hour). The appropriate combinations of variables are characterized by the concomitant formation of between about 0.8 and 3.5 weight per cent of gas lighter than butane and about 0.5 to 2.0 weight per cent of coke (the hydrocarbonaceous deposit on the The desulfuriz'ation may be effected using either static or moving bodies of catalyst, effective on stream times for the former being between 10 minutes and two hours, while eflective catalyst to oil ratios (pounds of catalyst charged to the desulfuriz'ation zone per hour per pound of oil charged to the latter per hour) gether with a single regenerator under the conditions disclosed and claimed in my copending application, Serial No, 752,211, filed June 3, 1947,

tinuation-in-part.

'I'he catalysts preferred for the desulfurization Such fractions are in considerable con- I of which application this application is a conoperation herein described are known to the art as active cracking catalysts. Such catalysts may be prepared by known methods and hence details of their preparation need not be repeated here. Typical catalysts are active or activatable clays or similar natural alumina-silicates (these materials having a final activity as defined below) or synthetic colloidal masses. Synthetic catalysts of this type should preferably have an alkali content of less than 1.0 weight per cent (calculated as NazO), and may be synthetic gels consisting essentially of silica together with one or more of the following refractory oxides: alumina, zirconia, thoria, magnesia, urania and the like, the silica generally being the predominating constituent. Other combinations of the above refractory oxides, such as zirconia-alumina, alumina-thoria, may be similarly used. Other solid active cracking catalysts may be used such as zirconium phosphate, but in any event, it is preferred that catalysts to be used in accordance with the invention be prepared to have an activity as measured by the CAT-A test of at least 25 and preferably over 30 or more. (The CAT-A test is a test method used commercially in the testing and evaluation of cracking catalysts; the activity of a catalyst being numerically equal to the volume per cent of motor gasoline formed when a standardized gas oil charge stock is passed over the catalyst at standard cracking conditions. The details of the test are given in Laboratory Method for Determining the Activity of Cracking Catalysts" by J Alexander and H. G. Shimp, page R-537, National Petroleum News, August 2, 1944.)

A considerable advantage may be gained in the present invention by using, as is preferred, a sulfur-resistant cracking catalyst. Many synthetic colloidal masses having cracking activity, such as the silica containing gels mentioned above, show such resistance in contrast to catalysts prepared by known methods from natural clays. Since variations in the source of the materials used and in the mode of preparation or treatment may result in variations in the sulfur-resistance of either natural or synthetic catalysts, it is more satisfactory to classify catalysts by an accelerated resistance test than by the previous history (as to source and type of preparation or treatment) of the catalyst. An accelerated resistance test which has proven satisfactory is to subject the catalyst to contact with substantially pure hydrogen sulfide at atmospheric pressure at a temperature of 1000 F. for two hours. Sulfur-resistant catalysts show substantially no decrease in catalytic cracking activity (as measured by the "CAT-A test referred to above) whereas catalysts which are not sulfur resistant show a decrease in catalytic activity of as much as 50 per cent.

By the use of sulfur-resistant catalysts in connection with the present invention, advantages may be gained in both fixed and moving bed operations. In fixed bed operations, the useful life of the catalyst is very considerably extended with a resultant savin in the cost of the catalyst. In operations in which the desulfurization zone forms a portion of a system com rising a regeneration zone through which system a fluent catalyst circulates such as in the form of a moving bed, the use of a sulfur-resistant catalyst eflects considerable economies in the cost of replacement of used catalyst by fresh catalyst when, in accordance with the invention, a high equilibrium activity, of above 25 and preferably above 30 as measured by the CAT-A test, is maintained in the system! by the addition of fresh catalyst of higher activity than the equilibrium activity (the equilibrium activity of the mass of catalyst circulating in a fluent catalyst system has a value fixed by the dynamic balance between the effect of adding fresh relatively high activity catalyst to replace catalyst lost or removed and the effect of deterioration of the activity ofthe catalyst in use).

In order to illustrate the present invention but not to be construed as a limitation thereof, the following examples are given:

EXAMPLE I Crude oil from the Slaughter field (west Texas) was distilled to yield a high straight run sulfur diesel fuel fraction having the following properties:

(a) This fraction was desul-furized in a fixed bed type of operation (alternate desulfurization and regeneration periods) using an active cracking catalyst in the form of beads of calcined synthetic low-alkali silica-alumina hydrogel (containin less than 25 weight per cent of A1203, and less than 1.0 weight per cent of alkali calculated as NaaO), preparedin a manner known to the art (see, for example, U. S. Patent No. 2,384,943, issued on September 18, 1945 to Milton M. Marisic, and U. S. Patent No. 2,387,596, issued on October 23, 1945 to Milton M. Marisic) and having a "CAT-A activity index of about 33. The catalyst at the start of the desulfurization period had less than 0.2 weight per cent of residual coke thereon. The conditions of desulfurization were: oil inlet temperat re, 855 F.; average catalyst temperature, 850 F'.'; pressure, 5 pounds per square inch pressure; length of run, 2.5 hours, space velocity, 1.0 (volumes of diesel fuel fraction at 60 F. per volume of catalyst per hour). In the desulfurization operation, the amount of gas lighter than butanes was 3.3 weight per cent of the diesel fuel fraction charged, the amount of coke formed being 1.6 weight per cent of the diesel fuel fraction charged.

The liquid products were distilled to yield a gasoline and a diesel fuel fraction, which had the following properties:

Octane Numbers:

0 R-M, clear CFR-R, clear Sulfur, weight per cent- Aniline point, "F Diesel index Octane number Yield, Volume per cent of diesel fuel fraction charged 1 Butane-Free.

(b) The same straight run diesel'fuel fraction was desulfurized in a similar operation under similar conditions except that the oil inlet temperature was 755 F. and the average catalyst temperature was 750 F., the amount of gas lighter than butanes and coke formed being 1.0 weight per cent of the diesel fuel fraction charged in each instance. The gasoline and diesel fuel fractions obtained by distillation of the desulfurized liquid product had substantially the 7 same properties as those listed in Table II;'the diesel fuel fraction having a lower sulfur content (1.03 weight per cent) but substantially the same diesel index and cetane number (46.9 and 48.8 respectively). The amount of butane-free gasoline formed in the desulfurization operation was. 18.1 volume per cent of the diesel fuel fraction charged.v f r g (0) Additional runs indicated that the sulfur content of the'diesel fuel fraction is insufliciently reduced (where more than 15 to 20 'per cent reduction is considered sufllcient reduction) when the desulfurization-conditions are such that the amount of butane-free gasoline formed is less than 10 volume per cent of the diesel fuel fraction charged and that, when the desulfurization conditions are such that greater than 30 volume per cent of butane-free gasoline is formed, the diesel index and/or cetane number ofthe desulfurized diesel fuel fraction is considerably depreciated.

(d) The effect of the sulfur content of the diesel fuel fraction was evaluated by subjecting a fraction from a Pennsylvania crude oil having approximately the boiling range of the diesel fuel fraction in Table I and a very low sulfur content (less than 0.1 weight per cent) to contact with the catalyst referred to above under conditions similar to those set forth in (a), such conditioi being adjusted so that the operation produced 28 volume per cent of gasoline (the amount produced from the high sulfur diesel fuel fraction). The diesel fuel fraction distilled from the liquid product obtained in this operation (initial boiling point 494 F. and end boiling point 685 F.) had a cetane number'6.5 units below that of the untreated diesel fuel fraction. Another run made under milder conditions to yield less gasoline than in the first instance also produced a diesel fuel fraction whose cetane number was lower than the untreated material.

EXAMPLE n A Wyoming crude oil (about 60% Elk Basin and 40% Frannie) wasdistilled to produce a wide cut distillate (a normally liquid light straight The light fraction was charged to the bottom of a reactor containing a moving bed of freshly regenerated cracking catalyst having less than 0.2 weight per cent of residual carbon thereon. The catalyst used was in the form of beads of 7 calcined synthetic low-alkali silica-alumina hydrogel prepared as set forth in Example I (a) and having a "CAT-A activity index of about 33. The light fraction was desulfurlzed under the following conditions:

Table IV Space rate, total charge 1. 2 Catalyst to oil ratio, based on total charge 014 Temperatures, F.:

Catalyst inlet 755 Oil inlet 750 Average of reactor 735 Catalyst outlet 725 Pressure, pounds/sq. in. gauge 9 Coke deposited on catalyst, weight per cent based on catalyst 1.0 C: and lighter, weight per cent of total oil charged 0.9 Coke, weight per cent of total oil charged 0.4 Liquid recovery, volume per cent of charge 102.2 The desulfurized light fraction was removed from the reactor and fractionated to yield products listed in the table below. The similar cuts occurring in the untreated light fraction are given for comparison.

Table -V DESULFURIZATION Diesel'fuel cut Gasoline 1 (boiling above gasoline) Properties In In In In Feed Product Feed Product Gravity, API 59.3 58.5 33.5 35.8 Distillation, ASTM, F.:

I it' 1 132 130 412 4l2 184 183 442 441 271 232 495 482 331 333 553 547 End point 313 ass .581 534 Octane Numbers:

CFRM. clear 50.4 58.2 CFR-R, clear 50.1 $0.3 +3 cc. TEL 37.3 78.2

Sulfur, weight per cent 0.10 0.02 0.93 0.57 Aniline Point, F 143 144 Diesel Index 52. 2 51. 6 Yield, Volume per cent of charge 50.4 58.2 49.6 41.0

1 Butane-free and washed with solution of alkali. As shown by the table above, the desulfurization produced a diesel fuel fraction whose sulfur content is about per cent lower than the original diesel fuel fraction, the diesel index of the treated fraction being substantially equal to the original fraction; and at the same time the octane number, lead susceptibility and sulfur content of the straight run gasoline in the'charge were considerably improved. This example shows that en- I tirely satisfactory results are obtained at temperatures below 800 F. and the use of such temperatures has been found to be especially valuable.

In the above examples, diesel index or cetane number has been used as a criterion of the quality of the hydrocarbon fraction treated. Since such a criterion measures, at least in part, the paraflinicity of a hydrocarbon fraction as well as the lack of branched chain structure, it will be understood that the present invention includes within its scope, the treatment of fractions that lie within the stated limits of boiling point so as to desulfurize these fractions while maintaining substantially constant paraffinicity. Thus tractor fuels, fuel for jet or gas turbine engines and the like, may be effectively desulfurized by'the processes herein described without increasing the aromaticity or amount of unsaturation.

Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from th spirit and scope thereof and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim as my invention:

1. In the production of high octane gasoline and diesel fuel from a straight run fraction of a petroleum crude oil, said fraction comprising a straight run diesel fuel fraction boiling in the range of 400 to 750 F. and having a sulfur content of at least 0.5 weigh percent: the process which comprises introducing said straight run fraction to a catalytic conversion zone wherein substantially all hydrocarbon material charged thereto boils below the end boiling point of said diesel fuel'fraction; contacting said straight run fraction in said conversion zone with an active cracking catalyst at mild conversion conditions of temperature, pressure, and contact time selected to effect conversion of said diesel fuel fraction to between about 10 and 30 volume percent of butane-free gasoline, an amount of dry gas lighter than butane of between about 0.8 to 3.5 weight percent, and an amount of coke between about 0.5 and 2.0 weight percent; removing hydrocarbon conversion products from said zone; and separating from said conversion products a gasoline fraction and a diesel fuel fraction, which diesel fuel fraction has a sulfur content substan-'- tially lower and a cetane number substantially as high as the untreated straight run diesel fuel fraction.

2. The process of claim 1 in which said straight run fraction contains straight run gasoline.

3. The process of claim 1 in which said catalytic conversion zone contains a moving bed of catalyst and is a portion of a catalytic conversion system through which the active cracking catalyst circulates and which comprises a regenera- REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,293,946 Payne Aug. 25, 1942 2,340,922 Bent Feb. 8, 1944 2,431,243

OTHER REFERENCES Cauley et al., National Petroleum News, vol. .37,-

No. 10, pages R--168, March 7, 1945.

Broom, Oil and GasJournal, vol. 39, No, 46,

pages 164-166, March 27, 1940.

Greensfelder et al. Nov. 18, 1947 

1. IN THE PRODUCTION OF HIGH OCTANE GASOLINE AND DIESEL FUEL FROM A STRAIGHT RUN FRACTION OF A PETROLEUM CRUDE OIL, SAID FRACTION COMPRISING A STRAIGHT RUN DIESEL FUEL FRACTION BOILING IN THE RANGE OF 400 TO 750*F. AND HAVING A SULFUR CONTENT OF AT LEAST 0.5 WEIGH PERCENT: THE PROCESS WHICH COMPRISES INTRODUCING SAID STRAIGHT RUN FRACTION TO A CATALYTIC CONVERSION ZONE WHEREIN SUBSTANTIALLY ALL HYDROCARBON MATERIAL CHARGED THERETO BOILS BELOW THE END BOILING POINT OF SAID DIESEL FUEL FRACTION; CONTACTING SAID STRAIGHT RUN FRACTION IN SAID CONVERSION ZONE WITH AN ACTIVE CRACKING CATALYST AT MILD CONVERSION CONDITIONS OF TEMPERATURE, PRESSURE, AND CONTACT TIME SELECTED TO EFFECT CONVERSION OF SAID DIESEL FUEL FRACTION TO BETWEEN ABOUT 10 AND 30 VOLUME PERCENT OF BUTANE-FREE GASOLINE, AN AMOUNT OF DRY GAS LIGHTER THAN BUTANE OF BETWEEN ABOUT 0.8 TO 3.5 WEIGHT PERCENT, AND AN AMOUNT OF COKE BETWEEN ABOUT 0.5 AND 2.0 WEIGHT PERCENT; REMOVING HYDROCARBON CONVERSION PRODUCTS FROM SAID ZONE; AND SEPARATING FROM SAID CONVERSION PRODUCTS A GASOLINE FRACTION AND A DIESEL FUEL FRACTION, WHICH DIESEL FUEL FRACTION HAS A SULFUR CONTENT SUBSTANTIALLY LOWER AND A CETANE NUMBER SUBSTANTIALLY AS HIGH AS THE UNTREATED STRAIGHT RUN DIESEL FUEL FRACTION. 